This invention relates to an epoxy resin composition for encapsulation of a semiconductor device, more particularly to an epoxy resin composition for encapsulation of semiconductor device, which can provide a cured product retaining a high glass transition temperature and which has a low modulus of elasticity as well as excellent humidity resistance and thermal shock resistance.
Generally speaking, it has been a common practice during manufacturing of resin encapsulated semiconductor devices to encapsulate semiconductor elements directly with a semiconductor-encapsulation resin.
In recent years, as the degree of integration has increased in the field concerning encapsulation of semiconductors, minute elaboration of various functional units on chip elements and enlargement of the semiconductor chip itself have likewise progressed rapidly. Due to the changes in these semiconductor chips, the encapsulation resins of the prior art can no longer satisfy present requirements. The epoxy resin compositions cured with a phenolic novolak resin, which have been employed in the prior art as resins for encapsulation of semiconductor devices, display excellent hygroscopicity characteristics high temperature electrical characteristics, moldability, etc., and thus represent the mainstream of the resins for molding.
However, when a semiconductor chip characterized by a large scale and a minute surface structure is encapsulated using this type of resin composition, the thermal stress strain generated by the difference in thermal expansion between the inner encapsulated material and the encapsulating resin may cause cracks on the phosphoric silicate glass (PSG) film or the silicon nitride (SiN) film, which is a coating material (passivation film) for protection of an aluminum (Al) pattern on the semiconductor chip surface. There can also occur cracks in the semiconductor chip, wire breaking of the bonding wire, and cracks in the resin molded product after encapsulation. In fact, the tendency for cracks to occur is very great when thermal cycle test is practiced. A decline in element characteristics can result due to chip cracking or to corrosion of the Al pattern caused by cracking of the protective film.
As countermeasures against such problems, it is necessary to increase the stress placed by the encapsulating resin on the inner encapsulated material, and also to increase adhesion of the encapsulating resin to the glass film (such as PSG film or SiN film) on the element. It is also required in the cured product to suppress the content of hydrolyzable halide compounds, particularly chloride ions, in order to minimize corrosion of Al pattern on the element surface, and also to maintain electrical insulating performance at a high level under humid or high temperature conditions.
To decrease the stress, a resin with small modulus of elasticity, low expansion ratio and low glass transition temperature should be used, but the glass transition temperature still must to be at a certain level or higher to obtain thermal shock resistance, particularly to prevent wire breaking of the bonding wire. Basically, it is necessary to maintain the glass transition temperature (150.degree. C.) of the encapsulating resin which has been employed for encapsulation of semiconductors in the prior art. But, if the resin is modified with a known flexibility-imparting agent for lowering modulus of elasticity, even when the effect of lowering in modulus of elasticity may be recognized, the glass transition temperature will abruptly be lowered to lower resistance to bonding wire opening. Also, when fillers are increased in amount for the purpose of lowering expandability, the coefficient of thermal expansion may be made smaller, but the modulus of elasticity will be increased, and moldability will also worsen due to increased viscosity. According to such prior art techniques, no encapsulating resin with a high glass transition temperature, low modulus of elasticity and low thermal expansion ratio could be obtained.